What a blast! Flying rock models save millions

Monday, 12 April 1999 C.Johnson, The Lab

Putting the science into the art of rock blasting

Dramatic 3D ultra-slow motion videos of exploding rocks and shock waves moving at 5000 metres a second are giving mining engineers unprecedented control over the once haphazard process of blasting the Earth.

The world-first technology developed by Australia's CSIRO allows engineers to "sculpt" the explosion of rock in methodical detail, ensuring the rubble drops in neat piles composed of the right-sized fragments, and generating the minimum dust possible.

The estimated savings amount to millions of dollars a day.

The technique could also improve the accuracy of some types of building demolitions, reducing the risk of accidents from flying debris.

Blasting is one of the most important activities in modern mining, and the cost of a poor blast can be high, says Dr Youzhi Wei of CSIRO Exploration and Mining.

"You get uneconomic sizes of rock fragments dumped in heaps that are expensive to dig," Dr Wei said. "You may get too little ore yield for your blast outlay. You may also get a lot of flying rocks and dust spread round the environment."

Yet for a long time, optimising the outcome of a blast has been regarded as more of an art than a science.

The new technique, trialled in the mining town of Kalgoorlie in Western Australia, allows scientists to model explosions based on "real life" rather than by using complex and often unreliable theoretical models.

The scientists starts by creating three dimensional maps of the rock to be blasted, taking into account its faults and fractures.

The maps are created by combining geological survey information with close-range photographs of the surface terrain that have been specially-treated to remove distortions.

Using two high speed cameras, the scientists then produce a 3D video which is used to measure the movement of the flying rock fragments. This is no mean feat as the shockwave moves about ten times faster than a flying bullet and the images from the two cameras need to be matched exactly.

The measurements are then used to calibrate the mathematical models predicting the results of blast designs.

For a given amount and configuration of explosive, these models predict the shape of the rock pile, the size of its fragments and the distance and direction of flying rock and dust.

Although developed for the mining industry, Dr Wei said the technology had applications for the safer demolition of concrete buildings using high energy explosives.

Better models would reduce the risk of accidents from flying debris like the one that killed a 12-year-old girl and injured nine others during the demolition of Royal Canberra Hospital in July 1997.